1. I start off with a mindblast.
2. Put vampiric touch and swp on the target.
3. Flaying until mb is off cooldown. Or have a fdcl proc and use it.
4. I always recast dots so they will always be on the target. Sometimes i miss one tick of swp or vpt. I do not know if this clipping is bad.
5. If i have 2 fdcl procs and mb is about to come off cooldown. I use the fdcl procs first to make my mb instant.
6. I use the shadowfiend off cooldowns and have all trinkets bound to dp.
7. Dp is onlu used with three orbs.

Can someone give me some advice to increase my dps. Compared to my friend who is playing an arcane mage. I feel my dps is very low.

1. I start off with a mindblast.
2. Put vampiric touch and swp on the target.
3. Flaying until mb is off cooldown. Or have a fdcl proc and use it.
4. I always recast dots so they will always be on the target. Sometimes i miss one tick of swp or vpt. I do not know if this clipping is bad.
5. If i have 2 fdcl procs and mb is about to come off cooldown. I use the fdcl procs first to make my mb instant.
6. I use the shadowfiend off cooldowns and have all trinkets bound to dp.
7. Dp is onlu used with three orbs.

Can someone give me some advice to increase my dps. Compared to my friend who is playing an arcane mage. I feel my dps is very low.

Thank you

Your problem is too much priority on FDCL. This proc should be one above MF in the list of priority and you should not interrupt MF to use a proc (though its ok to interrupt MF to cast MB). You should always use MB on CD that's the single most thing that will increase your dps by a significant factor. The glyph of MS isn't that great, a 1.5 sec cast is the same as having a instant cast with a 1.5 sec GCD so having your MB instant cast or not doesn't matter much.

ToF as a talent is good but if you want to test ur dps on a dummy then it'll never proc so your losing dps here get DI instead. You also never get to use SW meaning dps is always going to weaker on a dummy.

Try to use DPS cooldowns early and often only storing them up for Bloodlust / Heroism / Time Warp or Burn Phases.

'Complex' Priorities:
Alright, that was the SIMPLE version. With our current talents, abilities and mechanics there are many intricacies that the 'real' priorities list has a lot of qualifiers. Here you go:

Devouring Plague:
Because you only need to recast DPx3 before you generate your next SO you can do things such as refreshing DoTs or Halo or Shadowfiend... etc before you use this as long as it's cast before your next SO generator comes off CD. However if you spec into DI you should cast DPx3 immediately when it comes up in case you get a DI proc. The ONLY time you should use this with 2 SOs is if you currently have a temporarily high level of damage buffs that will expire before you generate your 3rd SO.

Mind Blast:
On CD, there is not any qualifier for this as unless you're currently casting a DPx3 this will be the most important spell to cast. More MBs in an encounter will likely be the best way improve your DPS.

Shadow Word: Death:
Now here is where the 'rotational' priorities get complex. Your FIRST SW cast in execute range will generate a SO and it will also reset the CD on SW allowing you to cast it a second time. This second SW will NOT generate a SO and is therefor lower on priority. You can think of the 1st SW = MB, while the 2nd SW is still a high priority you will often find yourself delaying it to cast MB or DPx3.

Mind Spike:
Proc'd to be free, instant cast and not to remove DoTs through FDCL. This can stack up to 2 times making the 2 stack MSp MUCH more important than the 1 stack MSp. Practically this translates into the 2 stack of MSp falling just below MB and SW, but the 1 stack of MSp falling below DoT refreshes with less than ~2 seconds left on duration / Halo / Shadowfiend / Mindbender.

Halo / Cascade:
Should be used pretty much only at the optimal distance as displayed by Halo Pro. For the average encounter you will not likely see a +/- 1 use of Halo or if you do not cast it exactly on CD, besides it's much better to hold onto it until a decent break in your rotation and you're at the proper distance.

For Cascade you want to save it for when you know it will hit multiple 'optimally' spread targets. This means multiple mobs far away from each other. Like in WotE when both Strengths and Rages are up, or in Elegon when Protector / Sparks / Foci are up.

Shadowfiend / Mindbender:
Similar to Halo you should find a decent break in your rotation to cast this. Also make sure that whatever you cast it on will be alive and damageable for the full duration.

If I have only 1 stack of MSp why break MF to cast it? There's no rush. If anything you'd wait for 2.

Also it's not bad advice. I didn't say anything that would make you lose dps.

Because breaking mf (as soon as it is right after a tick) doesn't make you lose any dps at all, and if you further down the road has to chose between e.g. casting the msp or refreshing dots that's a dps loss since you effectively traded casting mf for a sec in exchange for dot downtime/a msp.

Both ^this and not using the msp glyph will make you lose dps, that you don't understand why doesn't change the fact that it's bad advice.